1. Technical Field
The present invention relates to a zoom lens used for projecting an image produced by using a liquid crystal panel or the like on a screen, and a projector including the zoom lens.
2. Related Art
A zoom lens included in a projector in related art has first through sixth lens groups as a combination of negative, positive, positive, negative, positive, and positive lenses positioned from the front to the rear on the screen side, and fixes the first and sixth lens groups and shifts the second through fifth lens groups at the time of power change (see JP-A-2005-338702).
Another zoom lens in related art has first through fourth lens groups as a combination of negative, positive, positive, and positive positioned from the front to the rear, and fixes the fourth lens group) and shifts the first through third lens groups all in the same direction at the time of power chance (see JP-A-2001-188172).
A further zoom lens in related art has first through fourth lens groups as a combination of negative, positive, negative, and positive positioned from the front to the rear, and fixes the fourth lens group and shifts the first through third lens groups all in the same direction at the time of power change (see JP-A-2004-85979).
A still further zoom lens in related art has first through fourth lens groups as a combination of negative, positive, positive, and positive positioned from the front to the rear, and fixes the first and fourth lens groups and shifts the second and third lens groups at the time of power change (see JP-A-2001-124989).
According to the zoom lens disclosed in JP-A-2005-338702, however, the structure having the six lens groups is complicated. In addition, the half angle of view is 35 degrees or smaller, and the variable power ratio is about 1.4 times at most. Recently, there is an increasing demand for development of a projection zoom lens having a wider angle so that a large image can be projected in a small room. Moreover, development of a zoom lens having higher variable power ratio which provides higher degree of freedom for installation has been desired. Furthermore, miniaturization of the zoom lens and reduction of the number of constituent lenses have been important factors to be achieved so as to reduce the size and cost of the entire projection apparatus.
According to the zoom lens disclosed in JP-A-2001-188172, the F number is 2 at the wide angle end. However, the angle of view is small, and the number of the constituent lenses is large. In addition, the variable power ratio of the zoom lens is as small as 1.3 times.
According to the zoom lens disclosed in JP-A-2004-85979, the number of the constituent lenses is small and the angle of view is large. However, the F number is 2.5 at the wide angle end and thus brightness is insufficient under this condition. In addition, the variable power ratio of the zoom lens is as small as 1.2 times.
According to the zoom lens disclosed in JP-A-2001-124939, the F number is 1.5 at the wide angle end in the first example of the reference. However, the angle of view is small and the number of constituent lenses is large. According to the second example of the reference, the F number is 2 at the wide angle end and the angle of view is as large as 69 degrees. However, the variable power ratio is only 1.2 times.